Exactly. The Bird Cage “argument” is just a rehash of the “Watchmaker’s Argument”. Both of these rely on the willfully stupid premise that human beings can’t tell the difference between objects that are consistent with the natural world (e.g. living things that reproduce on their own, inanimate stuff like rocks and lumps of metals) and objects that have all the indications of being fabricated by another human being.

If human beings were designed, then we were designed really badly. Our hips and our spines make for painful upright bipedalism. Our birth canals are so freakin’ narrow that our babies have to be born with incompletely formed skull bones and kneecaps just so they’ll make it out alive. And if our bodies were designed by, say, the god of Christianity for specific purposes, why are we able to do all sorts of things that the god of Christianity prohibits?

For this argument to make sense at all, that birdcage would have to be just as twisted and obscure as the universe is, constantly surprising us wherever we look. (And hell, maybe it is forever expanding with black holes too for all I care.)

I’d love ask the theist if he though maybe someone could make a bird cage like that, and if so, how can it serve any purpose at all, except for just existing?

As an atheist(actually, nihilist is the right term for me), I wouldn’t just automatically assume that this obscure bird cage made itself, but it damn well might have!